1. Field of the Invention
The present invention relates to a method of controlling a recording magnetic field applied to a disk through a gap of a magnetic head in accordance with the recording density of the disk, and a magnetic disk apparatus therefor.
2. Description of the Related Art
A small gap of about 0.5 .mu.m may be formed in a read/write core of a magnetic head in a conventional high-density recording magnetic disk apparatus such as one using a vertical magnetic recording system. If the write current is not changed, the depth of magnetization is decreased as the gap length is shortened, as is the case with a high-density recording magnetic head. That is, when magnetic recording is performed by such a magnetic head, a recording magnetic field becomes relatively small, and the depth of magnetic recording becomes shallow as compared with a magnetic head used in a normal low-density recording apparatus, i.e., a magnetic head having a gap length of about 2 .mu.m.
In a high-density recording medium such as a barium-ferrite coating type medium, it is difficult to form a magnetic layer which is thin compared to a magnetization depth. For this reason, data is inevitably recorded in a surface portion of the magnetic layer. When in data is overwritten, previously recorded data may be left in a deep portion of the magnetic layer since a magnetic field, corresponding to data to be newly recorded does not reach a sufficient depth. This prevents an excellent overwrite characteristic.
In order to eliminate the above drawback, a magnetic head using a wide pre-erase system is employed in the above-described high-density recording magnetic disk apparatus. Data recorded in a track is erased by an erase head having a large gap prior to the data write operation. A strong erase magnetic field is generated by the erase head having the large gap. Thus, new data can be recorded after data in a deep portion of the magnetic layer has been reliably erased.
Such a high-density recording magnetic disk apparatus is required to be compatible with a low-density recording medium. When low-density recording is performed, the recording wavelength is elongated, and the minimum magnetization reversal interval is about 3 .mu.m. Since the magnetic head has a narrow gap for high-density recording as shown in FIG. 1, the recording depth remains shallow. If the ratio of a magnetization depth to the minimum magnetization reversal interval is decreased, the resolution of a reproduced signal may be degraded. Therefore, when low-density recording is performed using such a high-density recording magnetic head having a small gap, the reproduction resolution is degraded, and hence the reproduction of normal signals may become increasingly difficult.